Suvorov O. Charge transport in thin film superconducting heterostructures of MoRe–Si(W)–MoRe with a hybrid barrier from semiconductor with metal nanoclusters

The thesis is a study of peculiarities of charge transport in thin film superconducting heterostructures of MoRe–Si(W)–MoRe with a hybrid barrier from semiconductor with metal nanoclusters. Firstly, there are fabricated the thin film superconducting heterostructures of MoRe–Si(W)–MoRe with a hybrid semiconductor barrier with metal nanoclusters. Their transport properties have been investigated experimentally. The results of studies of silicon–tungsten Si(W) films obtained using an atomic force microscope in a noncontact mode indicate the presence of a quasiperiodic two-dimensional grid of tungsten clusters in them. It has been revealed (at nW < 4 at.% in the barrier) that on the heterostructures’ I–V curves the current resonant peaks appear which are caused by matching of the superconducting energy gap edge of electrode with a discrete energy level in the metal cluster inside the barrier. It was obtained (at nW ~ 7–10 at.% in the barrier) that the fabricated heterostructures become superconducting Josephson junctions with a resonance-percolating charge transport in them. These junctions have the increased values of the characterisitic voltage—it means the increased values of the ICRN product. These junctions are demonstrating large enough excess currents on the I–V curves so it evidence (in the frame of Belogolovskii–Shaternik–Shapovalov–Suvorov–Doring–Schmidt–Seidel model) that the transparency of resonance-percolating chains (through which charge transport appears) is close to unit. It was obtained (at nW~ 6–7 at.% in the barrier) that the heterostructures at TC < Т < 20 K demonstrate the conductance Gres decreasing (dGres(T) < 0, d(dGres)/dT < 0) and at Т > 20 K the conductance (Gres) increasing. In the frame of Kirpichenkov with coauthors model this evidence that there are quantum resonance-percolating trajectories in the N–I–N heterostructure barriers and that the single-impurity and double-impurity quantum shortcircuits contributions in the conductance of the dirty N–I–N junction become the main. It has been revealed that the obtained experimental IC(T) curves of the fabricated junctions have the positive second derivative d2IC/dT2(T). It means that in these junctions electron is tunneling through single or two discrete states in the metal clusters (resonancepercolating transport) and the resonance band is not narrow.